Mendel’s Laws of Heredity Why we look the way we look...

What is GENETICS? Genetics: the study of heredity Heredity: The passing on of characteristics (traits) from parents to offspring

Examples of Dachshund Traits Type of fur coat: smooth, long, wire Trait – A particular characteristic that can vary from one individual to another. Ex: hair color Examples of Dachshund Traits Type of fur coat: smooth, long, wire Color of fur coat: red, tan, black, silver

Fertilization Review! Fertilization: the joining of one male and one female gamete (reproductive cells) during sexual reproduction

GENES Genes - Section of a chromosome that determine the trait that will be inherited Ex: Sally has the gene for brown hair Each person two genes for each trait, one gene comes from mom, one from dad. Alleles - Different forms of one gene Ex: Brown, red, or blond hair are all different forms the hair color gene

Rule of Dominance Dominant gene: Always expressed if present for a trait Represented by a capital letter; “B” is for brown eyes. A brown-eyed organism could be BB or Bb to be dominant. The B for Brown eyes overpowers the b for blue eyes and so the organism displays the Brown eye trait. Recessive gene: Only expressed if two alleles are present for that trait Represented by a lowercase letter. “b” is for blue eyes. Organism must have genes bb to have blue eyes.

PRACTICE! 1. T T 2. t t _____ 3. T t 4. S S 5. s s _____ 6. S s Dominant Recessive Dominant Dominant Recessive Dominant

Homozygous vs. Heterozygous Homozygous: Organisms have 2 identical (same) alleles for a trait BB is homozygous dominant for brown eyes bb is homozygous recessive for blue eyes Heterozygous: Organisms have 2 (different) alleles for a trait Bb is heterozygous for brown eyes

Homozygous vs. Heterozygous

PRACTICE! 1. AA 2. Aa 3. Mm 4. gg 5. GG 6. Gg Homozygous Heterozygous

Phenotypes and Genotypes Genotype: (genes) the genetic makeup or combination of 2 alleles (1 from mom & 1 from dad) Ex. BB, Bb, bb Phenotype: physical characteristics of the trait Ex. Brown hair, blue eyes (what you see)

Genotype - always use the letter of the dominant trait first. Ex Genotype - always use the letter of the dominant trait first. Ex. Straight hair is dominant to curly hair Straight hair is dominant = capitol S Curly hair is recessive = lowercase s Genotype for straight hair = SS or Ss Genotype for curly hair = ss

A History of Genetics: Gregor Mendel Austrian monk Known as the Father of Genetics Cross-bred common pea plants to study the inheritance of traits through each generation.

Mendel’s Conclusions Biological Inheritance is passed from one generation to the next. Your traits are determined by genes passed toyou from your parents. Law of Segregation During Meiosis, the pairs of genes separate so that each gamete receives only one gene for each trait Law/Principal of Dominance Some alleles are dominant and some are recessive. Recessive traits will only show up if the dominant allele is NOT present

Punnett Squares Punnett Square - a diagram used to predict the outcome of a particular cross or breeding experiment. Used to determine the probability (chance) of EACH offspring’s genotypes and phenotypes. Does NOT determine how many offspring will be produced or exactly what the offspring’s genotype and phenotype will be…just the chances!

Punnett Squares There are five steps (you must always show your work) Key- List the trait, Both alleles, and which phenotype corresponds with each allele Parents- List the genotypes of each parent Draw the punnett square Determine the genotype ratio Determine the phenotype ratio

WW Ww Ww ww 1.W= wavy hair w= straight hair W w W w 2 3 2 ww = straight Genotype Ratio 1:2: 1 Phenotype Ratio 3:1 2 4 5

Practice Monohybrid Punnett! Cross a female heterozygous dominant brown eyes with a male homozygous recessive blue eyes X Possible Phenotypes: Possible Genotypes: Ratio: Percent:

Practice Monohybrid Punnett! Cross a female heterozygous dominant brown eyes with a male homozygous recessive blue eyes X B b Bb bb Possible Phenotypes: Brown & Blue Possible Genotypes: Bb, bb Ratio: 1:1 Percent: 50% Brown 50% blue b Bb bb b Bb bb